1. Field of the Invention
The present invention generally relates to corneal surgery, and is more specifically directed to an instrument including a lens having a linear incision guide for use in radial keratotomy procedures for reducing myopia and a tangential incision guide for effecting tangentially oriented incisions for astigmatic corrections. In both procedures precise control of incision depth is achieved by use of a mirror adjacent the incision area for permitting the surgeon to visually confirm and guide the corneal penetration depth of the scalpel being used.
2. Prior Art
Prior art devices do not allow the surgeon to control the incision depth by direct observation. In the prior art, the use of ultrasonic devices to measure the thickness of the cornea prior to surgery has been commonly used in an effort to afford the surgeon an indication of the corneal thickness. Such measurements, however, are plagued by significant errors because of the extremely small dimensions involved, leading to the currently observed and unacceptably high rates of corneal perforation.
Both radial and astigmatic keratotomy determine corneal cutting depth by use of an ultrasonic pachymeter, which maps corneal thickness in multiple locations on the cornea. Blade cutting depths approximately 98% of corneal thickness are usually required to produce desired corneal flattening and the tolerance for blade depth accuracy may be only as little as 5 microns. Unfortunately, the use of an ultrasonic pachymeter to set blade depth can result in large errors in incisional depth so that both overly shallow and excessively deep incisions are common. Thus perforations of the cornea are common as are overly shallow radial or transverse incisions which often reduce the effectiveness of the procedures. In fact, the inaccuracy of this step in these procedures is exemplified by the fact that the blade depth is usually set at 20 to 35 microns deeper than the ultrasonically measured corneal thickness in an effort to produce the desired effect.
Although radial and astigmatic keratotomy are facilitated by various radial, transverse and optical zone markers, the procedures are currently done free handed frequently producing errors in incision placement, incision length, incision direction and often inadvertent extension of radial incisions into the optical zone. Moreover, transverse corneal cuts often inadvertently extend into adjacent radial incisions, causing irregular astigmatism and wound gape.
The use of a slotted template as a guide for incisions in radial keratotomy surgery is known in the art; however, the procedures are currently done free handed in many instances. All of the teachings of the prior art, however, suffer from one or more flaws regarding inadequate control of the penetration depth and position of the incision.
U.S. Pat. No. 4,815,463 to Hanna discloses an apparatus for radial keratotomy surgery. The device uses a rigid template lens that fits against the surface of the cornea, molding it to the proper shape. The template lens has a plurality of slots for guiding the blades, and fits within a conical base member that is placed over the eye of the patient. The apparatus uses a vacuum to secure the cornea to the template. The incision blades are integrated directly into the device, and may be adjusted to vary the depth of the incision along the length of the cut. All incisions are made simultaneously.
U.S. Pat. No. 4,724,837 to Gannon discloses an apparatus and method for performing radial keratotomy surgery, the apparatus consisting of a cylindrical tubular housing, the lower end of which has a rigid multi-slotted incision guide template that fits against the cornea and conforms it to the proper shape. Scalpel blades are integrated into the device, and all incisions are made simultaneously.
A spring-loaded plunger brings the blades into contact with the cornea. Initial incision depth is set by adjusting the plunger stroke length. A second multi-slotted template is aligned with the corneal template to vary incision depth along the length of the cut. Roller bearings mounted on the sides of the blades contact the second template as the plunger is depressed, urging the blades outward from the center of the cornea to the ends of the template slots. By changing the thickness of the second template, the depth of incision can be varied along the length of the cut.
U.S. Pat. No. 4,688,570 to Kramer et al. discloses a simple, multi-slotted incision guide template for radial keratotomy surgery fitting directly onto the surface of a cornea and conforming it to the template's shape. The device has a cylindrical body, with inner and outer walls forming an annular chamber in which a vacuum is created to anchor the device.. to the eye. The device is employed in conjunction with a scalpel blade having guards which contact the upper surface of the template to prevent excessive incision depth.
U.S. Pat. No. 4,619,259 to Graybill et al. is directed to a device for radial keratotomy surgery having a slotted template guide that fits directly onto the cornea and conforms it to the shape of the template. Scalpel blades are integrated into the device in the form of a bladed disc positioned perpendicularly to the visual axis of the eye. The blades are actuated manually by a micrometer plunger assembly. Vacuum is used to ensure the device fits snugly onto the surface of the eye.
U.S. Pat. No. 4,526,171 to Schachar reveals a corneal incision device having a multi-slotted guide template, the lower surface of which holds the cornea in place and molds it to conform to the shape of the template. Used in conjunction with the device is a bladed disc, the depth of incision being controlled by a screw micrometer which advances the blades toward the incision guide and into the cornea. The bladed disc is spring-loaded to automatically retract when the screw micrometer is reversed.
U.S. Pat. No. 4,406,285 to Villasenor et al. discloses a template guide fitting over the surface of a cornea and conforming it to the shape of the template. Thickness of the template varies inversely with the thickness of the cornea immediately underneath it; the varying thickness controls blade depth penetration. Finger and thumb grips enable the operator to position the device over the eye.
Thus, a common problem with all of the prior art devices is that they do not permit continuous and/or accurate monitoring of the depth of the incision while the incision is being effected.
It is consequently the primary object of the present invention to provide new and improved means for permitting visual monitoring of incision depth in keratotomy surgery.
A further object of the present invention is a provision of new and improved means for accurately positioning radial and tangential incisions during keratotomy surgery.
Yet another object of the present invention is the provision of new and improved apparatus and methods for preventing tangential incisions from intersecting radial incisions during keratotomy procedures.
Another object of the invention is the provision of means for permitting the obtainment of precise desired corneal penetration during keratotomy procedures.